1. Field of the Invention
The invention relates to an adjustable length gas spring comprising a housing formed by an exterior cylinder and an interior cylinder and with a first end and a second end and a central longitudinal axis, the exterior cylinder having an inside wall and the interior cylinder having an inside wall; an overflow channel formed between the interior cylinder and the exterior cylinder; a piston disposed displaceably in the interior cylinder and dividing the interior cylinder into a first housing chamber and a second housing chamber, a piston rod mounted on the piston and disposed concentrically of the axis and extending through the first housing chamber and out of the housing; a piston rod guide and seal unit disposed at the first end of the housing and externally closing the housing chamber; at least one passageway permanently connecting the first housing chamber with the overflow channel; a valve disposed at the second end of the housing and closing the second housing chamber and provided for optional connection of the second housing chamber with the overflow channel, the valve having a valve body, which is disposed in the exterior cylinder by an outer surface concentric of the axis; which comprises a centering collar concentric of the axis for centering and holding the interior cylinder; which, in the outer surface, comprises an annular groove with a first outside seal that rests on the inside wall of the exterior cylinder; which, in the centering collar, comprises a second annular groove with a second outside seal that rests on the inside wall of the interior cylinder; which comprises a valve channel concentric of the axis; which comprises an annular groove with a first inside seal, the annular groove being open towards the valve channel and spaced from the second housing chamber; which comprises an annular groove with a second inside seal, the annular groove being open towards the valve channel and adjacent to the second housing chamber; which comprises a passageway permanently connected with the overflow channel on the one hand and with the valve channel on the other and opening into the valve channel between the first inside seal and the second inside seal; and which comprises a valve pin which is displaceable in the valve channel in the direction of the axis towards the second housing chamber, and which rests sealingly on the first inside seal and on the second inside seal when the valve is closed, and which bridges the second inside seal and connects the valve channel with the second housing chamber when the valve is opened.
2. Background Art
Gas springs of the generic type as known for instance from U.S. Pat. No. 3,656,593 comprise a valve having a valve body which, on its outside, is provided with two annular grooves for the accommodation of two outside seals, and with two annular grooves that are open towards the valve channel and house two inside seals. Mounting these four annular seals is extraordinarily complicated.
EP 0 383 303 A2 has taught to embody a valve for a gas spring of the generic type in such a way that a material suitable for sealing purposes is injection-molded entirely around a valve body, the function of the four seals mentioned thus being attained. A basic problem resides in that defined guidance of the valve pin and also defined guidance between the valve and the exterior cylinder and the interior cylinder is no longer achievable.